The present invention relates to a sintered Ti-based material product derived from injection molding of a powder material and a producing method thereof, in which the product can be provided with a mirror surface without any cloud by a finish machining of mirror-polishing.
Conventionally, a Ti-based alloy material required to have a mirror appearance has been used for exterior components of clocks or watches, for example. These components have been provided primarily by hot forging and machining of a material derived from the melting and casting process. But, those produced by the conventional method are inferior in the degree of freedom when designing since the forging is unsuitable for producing a product having a complicated form, and also be inferior in anti-scratch property since they must be provided with a limited low hardness for ensuring easy machining. Further, because they need a finishing allowance, the machining cost is expensive.
On the other hand, there has been known the metal powder injection molding (usually called "MIM") which is a method of producing a sintered body. The method comprises the steps of deforming feedstock by an injection molding machine, the feedstock consisting of a kneaded mixture of a metal powder and an organic binder; preparing a debinded body (brown body) by eliminating the binder from the molded body (green body) by means of an organic solvent or heating (herein below, this step is referred to as "a debinding process"); and heating the debinded body at a high temperature to obtain a sintered body.
The MIM is an excellent mass-production method of a three dimensional complicated form body made of a tough working material such as a Ti-based alloy. There is proposed in JP-A-7-90318 to produce a sintered Ti-based material product.
However, it has been impossible to provide excellent mirror surface to the conventional sintered Ti-based sintered MIM material because a white cloud can not be avoided even after finish mirror-polishing. While there are exterior components of watches as well as a watch frame, which are included in an item that is strictly required to have a mirror surface, until now there has not appeared the exterior components of watches made of the sintered Ti-based sintered MIM material in the market as an alternative of forged products.